Kinetic study reveals second-order oxidation of bromide by cobalt(III) species in acidic solution, highlighting rapid electron transfer via intermediate hydroxy complexes.
The cobalt(III) oxidation of bromide has been studied in the range 2–15° by the stopped-flow technique. In the acidity range 0·24–0·40M, the reaction has been shown to be second order, and is consistent with a mechanism both the cobalt(III) ion and its corresponding hydroxy-complex: Co3++ Br– [graphic omitted] CoII+ Br˙, CoOH2++ Br– [graphic omitted] CoII+ Br˙, 2Br˙ [graphic omitted] Br2 The rate constants k1 and k2 are 4·5 ± 1 and 770 ± 90 M–1 sec.–1 respectively at 7·5°, the associated activation energies being 22 ± 4 and 10 ± 3 kcal./mole. The reaction is considered to involve an SN1 process followed by the very fast redox step.
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Malik et al. (1970) studied this question.
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